Thin cover sheets, or veneers, made of a variety of materials, such as wood, metal, cloth, paper, and the like, long have been applied to various structural substrates for decorative purposes. Typical substrates are made of plastic, metal, wood, particle board, or other suitable materials. Generally, the decorative veneers are bonded to the underlying substrate through the use of various adhesives. When veneers made of relatively porous materials, such as cloth or paper, are used, care must be taken in the choice of the adhesives used to prevent unattractive bleed-through, or discolorations, resulting from the adhesive passing the veneer material.
Frequently, to ensure suitable bonding, it is necessary to employ thermo-setting adhesives which bond the decorative veneer to the underlying substrate through a combination of heat and pressure. Such processes are limited in the type and shapes of products which can be produced. Typically, high pressure applications are not suitable for the continuous formation of product.
Whenever adhesives are used to bond a decorative veneer or decorative surface film to an underlying substrate, de-lamination of the veneer or film from the substrate frequently takes place, after a period of time. This is a result of heat and moisture changes which produce different coefficients of expansion between the veneer and the underlying substrate, as well as changes which take place in the adhesive as it ages and as it is exposed to variations in heat and moisture.
The Kudo U.S. Pat. No. 3,960,639 discloses an approach for making a wood veneer covered metal substrate with improved bonding between the veneer and the substrate. In the Kudo patent, a non-woven cloth is impregnated with a thermo-plastic phenolic resin and then is placed between a flat metal facing sheet and flat sheet of veneer. Heat and pressure are applied to melt the adhesive and cause it to bond to both the substrate and the veneer surfaces. It is necessary, subsequently, to then stamp or otherwise shape the resultant product for its desired end use. The production of veneer covered metal substrates, in accordance with the Kudo process, is not suitable for a continuous operation.
Another patent directed to the utilization of a graphic print sheet on a rigid, flat panel is the patent to Goeden U.S. Pat. No. 4,746,560. The Goeden patent is directed to rigid fiberglass panels, which are impregnated with polyester resin, and which have an overlying resin-impregnated graphic print sheet on them. A transparent overlay layer placed over the printed sheet also is disclosed. The products of Goeden are used for flooring material, or for wallcoverings. Goeden requires the lamination to be formed by placing base mats in a press with the print and a cover sheet, or veil, placed on top of the print layer. The press then is closed at approximately 500 psi at 220.degree. F. for several minutes. This clearly is not a continuous process, although the resultant product is a strong composite panel, with a decorative image on the exposed surface.
The patent to Kiss U.S. Pat. No. 4,655,861 discloses a continuous process for producing strips of products having a substrate which is bonded to a decorative surface. In Kiss, a protection sheet and a decorative sheet are moved past a station where the side of the decorative sheet not covered by the protective sheet is coated with an adhesive. A mixture of fibers and thermo-plastic binder is applied to the adhesive on the protective sheet. The sheet with the fibrous layer then is passed between calendar rolls to compress it. After this step, the product is cut to the desired shape and is finished in a heated compression mold, to form the sheet into an end product, and to soften the thermo-plastic binder in the designed for use as automobile panel coverings.
The patent to Barrell U.S. Pat. No. 4,803,022 is directed to a continuous process for producing metal foil laminates, used subsequently for manufacturing printed circuits. The metal foil is directly bonded to a sheet of fiberglass reinforced polyester and epoxy resin. To form the resultant laminate, a layer of polyester and epoxy resin is applied to copper foil. This layer also may contain an adhesion promoter. Chopped glass fibers are randomly distributed into the resin layer, and the laminate is subjected to heat treatment to initiate gelation. After gelation, the laminate is cured to bond the substrate thus formed to the metal foil. The curing step utilizes radio frequency electromagnetic energy to raise the temperature of the laminate for improving the bonding of the substrate to the copper foil. The final curing step is not part of the continuous process, but is accomplished in a batch process after desired lengths of the laminate are cut from the strip formed in the initial continuous stages of the process.
The patent to Prince, et al U.S. Pat. No. 4,818,590 is directed to a rigid plastic foam substrate which has a thin wood veneer adhesively bonded to the substrate to form a variety of decorative products, suitable for venetian blinds, furniture panels, room dividers, and the like. The patent is specifically limited to rigid polyvinyl chloride substrates, or comparable products, to which thin wood veneer panels are bonded by means of wood adhesives or heat lamination adhesives. The veneer is chosen to be very thin compared to the thickness of the substrate. The product which is disclosed in the Prince patent is similar in appearance, and is constructed in a similar manner, to the known metal/wood veneer products of the past. The physical characteristics of the underlying plastic, however, essentially are matched to those of the wood veneer, to avoid the problems of separation, cracking, and the like, which occurred with earlier metal/wood veneer laminated products.
Lineal structural fiberglass members made by pultrusion are disclosed in the patents to Hindersinn U.S. Pat. No. 4,419,400; Carter et al U.S. Pat. No. 4,681,722; and Thorsted U.S. Pat. No. 4,842,667. No decorative veneers are disclosed in these patents.
Although a variety of products are disclosed in the prior art, as typified by the patents mentioned above, where a decorative surface is applied to an underlying substrate, none of these prior art structures have a decorative surface which constitutes an integral part of the substrate itself. Accordingly, it is desirable to provide a process which creates a unitary structurally strong product in which a decorative surface layer is an integral part of an underlying supporting substrate.